There has been a known technology in which when a communication device of a calling party transmitting a signal to a communication device of a communication partner receives a retransmission request of signal from the communication device of the communication partner, the communication device of the calling party upon receiving the retransmission request retransmits the signal to the communication device of the communication partner. Hereinafter, the communication device of the calling party which transmits a signal to the communication device of the communication partner is referred to as a “communication device A”. Also, the communication device of the communication partner which transmits the retransmission request of signal to the communication device A is referred to as a “communication device B”
Related techniques are disclosed in, for example, Japanese Laid-Open Patent Publication No. 2007-150859, Japanese Laid-Open Patent Publication No. 2008-219408, and International Publication No. WO 2004/107639.
In the related art, however, there is a concern that the communication speed between the communication devices may be reduced due to the retransmission of signals by the communication device that received the retransmission request.
FIG. 9 is a diagram illustrating an example of a retransmission issue of signal in the related art. In the example of FIG. 9, the communication device A is a base station and the communication device B is a mobile terminal. FIG. 9 illustrates the state of the communication between the communication device A and the communication device B in a chronological order. Further, the details of the state of the communication illustrated in FIG. 9 are described in Chapter 11.5.2. of GPP TS 25.322 V10.1.0.
First, the communication device A transmits signal “a” having a sequence number of 0 (zero) to the communication device B (step S1). It is assumed that the signal “a” arrives at the communication device B. Subsequently, the communication device A transmits signal “b” having a sequence number of 1 (one) to the communication device B (step S2). It is assumed that the signal “b” does not arrive at the communication device B. Subsequently, the communication device A transmits signal “c” having a sequence number of 2 (two) to the communication device B (step S3). It is assumed that the signal “c” arrives at the communication device B. Subsequently, the communication device A transmits signal “d” having a sequence number of 3 (three) to the communication device B (step S4). It is assumed that the signal “d” does not arrive at the communication device B. Subsequently, the communication device A transmits signal “e” having a sequence number of 4 (four) to the communication device B (step S5). It is assumed that the signal “e” arrives at the communication device B.
In the meantime, the communication device B which has received the signal “c” detects that the signal “b” has been missed and transmits a retransmission request of the signal “b” to the communication device A (step S6). The communication device B which has received the signal “e” has not yet received the signal “b” and signal “d”. Therefore, the communication device B detects that the signal “b” and signal “d” are missed and transmits a retransmission request of the signal “b” and a retransmission request of the signal “d” to the communication device A (step S7).
The communication device A which has received the retransmission request of the signal “b” transmitted at step S6 retransmits the signal “b” to the communication device B (step S8). It is assumed that the signal “b” arrives at the communication device B. The communication device B which has received the signal “b” has not yet received the signal “d”. Therefore, the communication device B detects that the signal “d” is missed and transmits a retransmission request of the signal “d” to the communication device A (step S9). In the meantime, since the communication device A which has received the retransmission request “b” and the retransmission request “d” transmitted at step S7 has received the retransmission request of the signal “b” again although the communication device A has retransmitted the signal “b” at step S8, the communication device A retransmits the signal “b” to the communication device B (step S10). The communication device A retransmits the signal “d” after the retransmission of the signal “b” at step S10 (step S11). In the meantime, since the communication device A which has received the retransmission request of the signal “d” transmitted at step S9 has received the retransmission request of the signal “b” again although the communication device A has retransmitted the signal “d” at step S11, the communication device A retransmits the signal “d” to the communication device B (step S12).